There is widely known a feedback control that brings an air-fuel ratio, which is a ratio between air and fuel in an exhaust gas exhausted from an internal-combustion engine, close to a target air-fuel ratio so as to improve fuel efficiency of a vehicle, and this air-fuel ratio is detected by an air-fuel-ratio sensor (A/F sensor).
As for an air-fuel-ratio sensor, there is known an air-fuel-ratio sensor that controls a current and a voltage to a plurality of terminals connected with a gas sensor element so as to detect an air-fuel ratio. With regard to this air-fuel-ratio sensor, there is proposed a technology that detects abnormalities of a ground fault and a sky fault of these terminals on the basis of voltages of the terminals connected with the gas sensor element (for example, Japanese Laid-open Patent Publication No. 2005-291991).
However, when states of the voltages of the terminals connected with the gas sensor element are sampled at predetermined time intervals so as to detect an abnormality of a ground fault or a sky fault, a load for detecting the abnormality becomes large.